Where each sign comes from

About 2,500 years ago, Babylonian astronomers divided the band of sky along which the Sun, the Moon and the planets move into twelve equal parts and named each one after a constellation. The Greeks added the stories: almost every figure in the zodiac has a myth behind it.

It helps to keep two things apart. Constellations are groups of stars of very different sizes. Signs are twelve 30-degree sections that start at the spring equinox. When the system was fixed, signs and constellations almost matched. Today they do not, because of a slow wobble of the Earth's axis called precession: the Sun enters the sign of Aries while it is in front of the constellation Pisces. Western astrology uses the signs, not the constellations.